text:
Can an aerodrome in class G airspace be controlled?
Can an aerodrome be controlled, even if the only associated airspace is classified G?
E.g. can such an aerodrome have a control tower with the authority to give takeoff and landing clearances and taxi instructions?
I know the opposite is possible (uncontrolled aerodromes in class D airspace for example).
I am not asking about AFIS aerodromes, since AFIS is not an air traffic control service.
Please provide examples and/or references to ICAO SARPs or national regulations.

Are you asking about a specific country or set of regulations? ICAO doesn't make regulations directly, it's up to each country to do that.

ICAO makes Standards and Recommended Practises. ICAO Standards do not preclude the development of national standards which may be more stringent than those contained in an Annex. My question is about ICAO Standards as outlined in the Convention on International Civil Aviation (Chicago 1944) and its annexes.

Under FAA the answer is "yes".  So the question is "why not classify it as Class D?" The reason is that a Class D airport must have a certain level of weather reporting, and these controlled Class G airports dint comply

Ref http://aviation.stackexchange.com/a/21900/3504

Well, sort of.
In Class G airspace you often find ATZs. This is airspace 2nmi radius to 2,000ft around an aerodrome that is controlled by the aerodrome so take-off and landings. They are often not surrounded by Class-A or Class-D airspace and just control the immediate area around the aerodrome, and are full ATC unit, although sometimes only an AFIS.
So, there is a little controlled airspace associated with it, but very little. An aircraft must have permission to penetrate it.
In the UK a clear example is EGCL (Fenland).
However, if you count this as too much controlled airspace for your question, then no.
It would not be practical to control landings or take-off when the aircraft is immediately in uncontrolled airspace.

In fact, according to https://www.bfgc.co.uk/VFR_Guide.pdf, "An ATZ conforms to the Class of Airspace in which it is situated thus, for example, in Class G Airspace Rule 45 will apply but in Class D Airspace the requirements of Class D will apply in addition (UK AIP section ENR 1.4 refers)." If I'm reading that correctly, an ATZ would still be classified G if it was situated in G airspace.

Great find! Thanks! I think that is mostly for ATZs inside higher class airspace (so rules for class-D apply) but very interesting! Aircraft still need the ATSU permission to penetrate the ATZ though.

I must say that I've never seen the phrase "numerous ditches" on a chart before. So I'm confused, in a class G ATZ does the tower have "the authority to give takeoff and landing clearances and taxi instructions?" If so, why not just make it class D?

@TomMcW No, the ATSU within an ATZ does not have control over takeoffs and landings. You need permissions to penetrate an ATZ, this permission can either be bound to certain requirements (transponder, type of aircraft, color of your underwear) or to the requirement to establish a two-way communication with the ATSU of the ATZ airfield.

You can find ATZs inside higher class airspace, but not always remember.

@SentryRaven Sometimes, ATZs provide a full ATC service, so do control landing, sometimes only an AFIS or A/G is provided so do not. https://members.gliding.co.uk/library/airspace/atz-procedures/

@D.Clayton Ah, I forgot that the UK have taken ATZs to a new level...

An airport in class G airspace can have an operating control tower. This is a case of a towered airport in uncontrolled airspace. The airspace is uncontrolled but tower communication must be established within a certain distance and for use of the airports runways.
There are applicable regulations that address this situation. 14 CFR §91.126 (d) requires pilots to establish and maintain communication with a Class G towered airport before entering a 4 NM radius below 2500 AGL.
As of today, Lake City, Florida (KLCQ) is an example of such an airport, although that will change at some point in the future.

Great example, thank you

It looks like KLCQ won't be class G for much longer. Interestingly, the Chart Supplement, IFR en route chart and Garmin Pilot all say already that it's class D to 2500'.

@Pondlife Thanks I updated the answer to reflect that new information.

The A/FD describes the airspace around KLCQ as class D when the tower is in operations, despite what is shown in the chart.  It may be represented this way on the VFR sectional due to the fact that KLCQ tower operations can be closed outside of the normal posted hours and that CTAF should be monitored by traffic.

Thanks @CarloFelicione. I'm not sure if the class D when operations in effect is new or not, but the 14 CFR §91.126 (d) does describe required procedures for operations at a class G airport with a control tower. Whether KLCQ fit that bill now or in the past, the reg is there and the situation can arise.

No.  By definition, Class G airspace is uncontrolled.  The airport would have to be in a minimum of Class D airspace for it to be controlled.

Do you have any official reference? I am not asking about the air above the aerodrome, but the aerodrome itself. I know examples of uncontrolled airfields within class D airspace, so it seems there may not be a direct correlation between airspace class and whether or not an aerodrome is controlled.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/phak%20-%20chapter%2014.pdf. ATC has no authority nor requirement to regulate class G airspace.

Just watch the NOTAM, in some cases (military deployment, ..) the class G airspace can be very quickly "reclassified" to the class D space. But - you're right, it's not class G anymore.

@CarloFelicione Class E airspace can go to the ground too but the AIM states that that pilots should contact the tower if it is in operation, even if the towered airport exists in class G airspace. A good example of this, in addition to the one is the Houston Executive Airport (KTME) - flew in there the other day and they have a tower and even separate ground and clearance delivery frequencies but the airspace is class G to 700' AGL.


text:
Why can we not use full throttle in a C172 when cruising at lower altitudes?
My flight training manual (FTM) says that at low altitudes we throttle back our trainers in order to not exceed recommended power settings. We use the Lycoming O-320 engine.
But why is that?
Is the air close to sea level just too dense for the standard Cessna 172 engine?
And at 8000 feet it's just thin enough for us to cruise at full throttle?

What is FTM?  The question could be improved by explaining.  Flight Training Manual?  If so, which one?  Some are better than others.  Also there were at least a couple of grammatical errors in this question, some of which have now been corrected.  Also please explain in more detail what you mean by "the normal Cessna engine".  Also consider modifying your title so that it actually asks a question, the same question that is filled out in more detail in the body of the question.

It would be helpful to know what engine we are talking about. I once flew a C172 that had a Porsche engine.

Aaron, the engine is Lycoming O-320.

@leha007 you should put any relevant information in the question, not in comment.

These engines are not designed to run at maximum horsepower output all the time with a lean mixture.  They are designed to cruise at 50-75% of their rated max power, and deal with that level of internal heat and friction over the long term.  Even this is fairly hard compared to a car that runs at perhaps 20% of rated power when cruising at 60 mph.
Running them wide open means maximum heat, maximum wear, for not much benefit considering the power required to go faster is nearly the cube of the speed increase. You must run with the mixture full rich to keep the engine cool at all, and fuel burn is a lot higher because you are dumping unburned fuel used for cooling at full power out the exhaust.  It's not worth it in other words, unless you are racing, so the concept of cruising at not more than 3/4 of rated max power is a very old convention in piston engines, and mixture leaning shouldn't really be done above that.
You can run one of these engines at full throttle with a rich mixture with the RPM near red line all the time if you want, but only if you don't mind paying for the 20 thousand dollar premature overhaul from flogging the poor engine like a mule (the exhaust valves will hate you for all eternity).
It's pretty much the same thing as hooking up a big heavy trailer to your car, that required foot on the floor all the time just to stay at highway speed.  How many miles do you think that car's engine would last?(Although the Lycoming being run that hard will still probably outlast the car engine in the same shoes.)
However, when you go up, by the time you get to 8000ft, 75% of maximum output is all that is available with wide open throttle (WOT) in the thin air, so 75% cruise, normal operation, requires WOT and no harm is done. And as you go up further, you find you can't even get 50% with WOT and pretty soon you're at your service ceiling.

John, Do you mean at at low altitudes, our engine is able to produce close to(if we disregard the internal friction) 100% BHP due to the dense air, but it is designed to run at 55-75 for better cooling/less wear etc`?                 And as we go higher, say 8000 feet, due to the thin air, our engine is only able to produce 75% compared to what it can at sea level, and for that reason we use the throttle full open?

Yes.  75% requires, depending on the RPM, somewhere around 22-23" of manifold pressure (you don't normally get a MP gauge with fixed pitch props). WOT gives you just under ambient atmospheric pressure in the intake manifold due to the residual restriction of the carb venturi and throttle plate etc. If the barometer says 30" of mercury at sea level, WOT will give somewhere around 28-29" in the intake passage.  At 8000 ft the ambient is down to around 22-23" so the best you can get is maybe 21" at WOT, just enough to make 75% at the RPM you will see at that altitude at WOT (just below redline).

thank you John.

the Lycoming being run that hard will still probably outlast the car engine in the same shoes - really? I consider the car engine an absolute marvel of reliability considering the abuse they get - owners forgetting to service cars for tens of thousands of miles past their dates, flogging them through dirty atmospheres with all sorts of contaminants splashing all over them, precious little steady state running.. Aircraft engine would probably quickly die in a car, and maybe fortunate that Honda don't make aircraft engines; they'd put everyone in the service industry out of work! :)

@CaiusJard I've seen videos of idiots revving lamborginis in traffic til they catch fire. Same idea.

Not really.  If you've ever had a Lyc apart the difference structurally is quite striking. And the car engine spends its life at 20% of rated power or less, with brief spurts higher, and almost never at WOT.  You have to be racing it to get it to an equivalent load.  There are aircraft conversions of Honda Civic engines out there, and they do ok although they need a reduction drive, but they wear out at 1000 hrs and won't run 2000-3000 hours like a Lyc will.  A/c engines are more like industrial or tractor engines.

I made some edits because I should have mentioned how mixture leaning figures into it.

If you are well past best L/D, the power goes up with almost the cube of speed. Underscores your point that it isn't worth it.

I was going to mention that it's the cube, not the square. Drag is approximately proportional to speed squared, and power is proportional to drag times speed.

Thanks for the input you two.  I made a little edit.

Most Cessna 172s have fixed-pitch propellers. Designing a fixed-pitch prop always requires making some compromise between climb performance and cruise performance. Typically this means that at low altitude in horizontal flight, at full throttle the engine would exceed redline RPM, so you have to throttle back. At higher altitude the engine produces less power at a given RPM, so it isn't a problem there. It's possible to use a "cruise prop" that has a coarser pitch and allows full power (or closer to full power) in low altitude cruise, but this comes at the expense of not making full redline RPM at the start of the takeoff roll, and therefore lower acceleration and longer takeoff runs.
Variable-pitch propellers (of which "constant-speed" propellers are a subset) avoid this dilemma, though they have their own downsides such as increased complexity and a bunch of extra weight right on the nose where you don't want it.

I agree with the above answers in terms of the limitations related to engine. However I wanted to also add that it could be possible that going full throttle at a low altitude would cause the aircraft to go out of its structural flight envelope as well. So as much as being an engine related issue, it could also be due to structural considerations of the airplane.

Not in level flight on a 172.

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text:
When must delegated airspace be listed in the AIP?
Two states can agree, through a bilateral letter of agreement, to delegate the responsibility for providing air traffic services (ATS) within a certain airspace from one state to the other. There can be numerous reasons for this. For example, a part of Scottish airspace is delegated to the Danish air navigation service provider (ANSP), because Denmark has better radar coverage within the specific area. In this area, which is within Scottish airspace, ATS is provided by the Danish ANSP.
My question is regarding the need to publish details about such airspace delegations in the national aeronautical information publications (AIP).
The previously mentioned delegated airspace is described in AIP Denmark section ENR 2.2 (Other regulated airspace). However, a part of German airspace within Hannover upper flight information region (UIR) is also delegated to Denmark, but this airspace is not shown anywhere in the AIP. To me, this seems very inconsistent, which brings me to my question: under which circumstances are states required to publish information about delegation of ATS? I am interested in references to ICAO SARPs or PANS, or, alternatively, EU regulations.
The below chart (AIP Denmark ENR 6.2 – 1) clearly indicates some delegated areas in Scottish airspace and around the border to Sweden (which I have marked with blue), but, the delegated area in Germany (which I have marked with red) is not shown.

The area is, however, shown on this "Sector Boundary Structure Chart" chart published by Eurocontrol:

I have looked in ICAO Annex 4 and Annex 15 without any luck.
Appendix 1 of Annex 15 states that:
ENR 2.1 shall contain, among other things:

Detailed description of flight information regions (FIR), upper flight information regions (UIR), and terminal control areas (TMA), including:
  (…)
  2) identification of unit providing the service;
  (…)

I usually see delegated airspaces listed in ENR 2.2, though, so they do not seem to need to be covered in ENR 2.1.
ENR 2.2 shall contain:

Where established, a detailed description of other types of regulated airspace and airspace classification.

It is not specified exactly what this includes.

I hope someone, maybe DeltaLima, will provide more information. In the meantime I've posted what I found.

Principles under ICAO agreements
Delegation of ATC services is contracted between ICAO members using bilateral or multilateral letters of agreement. Cases of such delegation exist typically to cover remote large airspace (e.g. Arctic agreement between multiple countries), or small areas (e.g. islands).
ICAO members are committed to fulfill the decisions of their constituent act, the Chicago Convention signed in 1944. Among the annexes to the Convention, annex 15 is related to the provision of aeronautical information services (AIS):

Annex 15 defines how an aeronautical information service shall receive
  and/or originate, collate or assemble, edit, format, publish/store and
  distribute specified aeronautical information/data. The goal is to
  satisfy the need for uniformity and consistency in the provision of
  aeronautical information/data that is required for the operational use
  by international civil aviation.

Impact on AIP
Annex 15 includes these generic articles:

3.1.1.2 Each Contracting State shall take all necessary measures to
  ensure that the aeronautical information/data it provides relating to
  its own territory, as well as areas in which the State is responsible
  for air traffic services outside its territory, is adequate, of
  required quality and timely. This shall include arrangements for the
  timely provision of required information/data to the aeronautical
  information service by each of the State services associated with
  aircraft operations.

and

3.1.7 An aeronautical information service shall receive and/or
  originate, collate or assemble, edit, format, publish/store and
  distribute aeronautical information/data concerning the entire
  territory of the State as well as areas in which the State is
  responsible for air traffic services outside its territory.
  Aeronautical information shall be published as an Integrated
  Aeronautical Information Package.

I was not able to find the decision to use AIP ENR 2.2 (other regulated airspace), but it's a matter of fact the information is found here, e.g. in the Norway AIP:

5: Delegation of Responsibility for Provision of ATS
5.1: General Denmark, Norway, Sweden and the United Kingdom have
  arranged through the exchange of bilateral Letters of Agreement to
  transfer the responsibility for provision of ATS within parts of their
  own area of responsibility, to their neighbouring State.
Procedures and communication within the said areas will be as if the
  airspace was an integral part of the FIR for which the nation
  mentioned is responsible.

Bidirectional scope
An effect of these articles is both the delegating and the providing states shall publish information about related areas. For example in the Spanish AIP, two cases are described.
Spain delegating to Portugal:

By agreement between Sevilla ACC and Lisboa ACC, the air traffic
  service is provided by Lisboa ACC within the airspace defined by [...]

Spain receiving delegation from Portugal:

By agreement between Lisboa ACC and Madrid ACC, the air traffic
  service is provided by Madrid ACC within the airspace defined by [...]

So according to ICAO, there does appear to be any obvious reason why the example delegation in my question is not listed in the AIP - but nothing explicitly says that it is required, either. Thanks for digging this up!

@J.Hougaard: My understanding is it must ("shall") be in both AIP, German one because it's their territory (3.1.1.2) and Danish because they provide services outside their own territory (3.1.1.7). Now if the information doesn't say about the delegation but does provide all operational elements, then it may be acceptable not to disclose the delegation, but this is not obvious from the texts above.

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text:
What's the formula to calculate static air temperature?
What's the formula to calculate external temperature (static temperature) of an aircraft, given that I have Mach, TAS and altitude?
Since I don't know the formula, I tried to search on Google. But I found that I need total air temperature, which must be know by a sensor (and I don't know). So, is there any other formular/way to calculate static air temperature using only mach/tas/altitude, or is not possible with only these data?

welcome to aviation.se. what have you tried?

Since I don't know the formula, i tried to find in google. But I found that I need total air temperature, which must be know by a sensor (and I don't know). So, is there any other formular/way to calculate static air temperature using only mach/tas/altitude, or is not possible with only these data?

thank you for the clarification, I've added the details to your question.

is there any other formular/way to calculate static air temperature using only mach/tas/altitude ?

No.
Mach (or TAS) can only give you the ratio between total and static air temperature, as seen also on Wikipedia:
$$ \frac{T_\mathrm{total}}{T_{s}}={1+\frac{\gamma -1}{2}M_a^2} $$
Knowing the Mach number will give you the quantity on the right hand side of the equation ($\gamma$ is constant and is about 1.4 for dry air). If you cannot measure one of the two quantities on the left hand side, you cannot derive the other.
You could in theory derive the temperature from a measurement of the static pressure, if somehow you could also measure the air density, but that's not using only "mach/tas/altitude" as you requested.
A final option is to derive the temperature from the standard atmosphere model using the altitude, but that might not be a number reliable enough for your purposes.

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text:
What vintage aircraft was registered as NC7210?
Can anyone help identify this vintage aircraft, origin, and possible flight history. Airplane has this number of its wing, NC 7210.

Do you have a picture of this airplane? Or more information? It's difficult to answer without more to go on.

@VtC - It seems pretty clear what's being asked. It may not have been asked well, but with (currently) 2 answers pointing at the same thing, it seems perfectly clear...

@FreeMan Registration numbers can be reused, can't they? So the plane identified by the two answers isn't necessarily the one the asker is thinking of.

My step grandfather, Roy Danischefsky, purchased the Ryan B-1 Brougham #157 NC 7210 in Sept 1928 from Mahoney-Ryan Aeronautics for Midwest Airlines (Wisconsin). He flew it for Mid-West as a private charter and to promote flight as a new transportation option. Here is a photo of him in front of the plane.
Also - Here a photo of the plane from San Diego Air and Space Museum Archives
https://www.flickr.com/photos/sdasmarchives/5684139991/in/photostream/
Where is this plane now? I would be VERY EXCITED to know that it is still exists. Many of these planes did not survive.

Welcome to Aviation.SE and thanks for sharing your story. If you want to know where this plane is now, it would be best to ask that as a separate question (you can link to this one for context).

There is (or was) a Ryan B-1 Brougham of construction number 157 registered as NC7210 according to airhistory.org.uk.

This registration record page says it's a Ryan B-1 Brougham.  That's the same company that built the Ryan Lindbergh flew solo across the Atlantic, though it's a different model aircraft.  The page linked says a couple aircraft of this model were used in a Lindberg movie, flown by the late Paul Mantz.


text:
What happens to US military demo teams following unexpected pilot turnover?
Following up on recent events involving the Blue Angels and the Thunderbirds, what is the typical procedure for these teams following a unexpected turnover of a pilot (in this case, a fatal or other serious crash)?
Do these teams have a "B" team in training to pull talent from, or possibly have a larger pilots roster that will rotate in and out throughout the season to pull from?  Maybe even have multiple teams that trade off show duties and training during the season?
(I assume that the Thunderbirds will just paint up a new plane and give the pilot a good pep talk).

I'm pretty sure the military takes accidents more seriously than a 'pep talk'.

@DJClayworth, Oh for sure, they won't be flying for the next few weeks at least, but should nothing else serious turns up, then they could be by the end of the summer.  I just didn't want too much talk on on the loss of the aircraft affects it (FYI for the stumbler:  the Thunderbirds F-16s are straight combat stock with a few changes).

I can't answer for the Blue Angels or the Thunderbirds, but I can for the UK equivalent, the Red Arrows.
The Red Arrows have no spare pilots (or 'B team'). The nine pilots on the team fly every display in their 3 year tour. The explanation is that a spare pilot would not fly frequently enough to be current and safe. They do however have the capability to do an 8-plane display (rather than the usual 9) which they can use if a pilot is temporarily incapacitated. They also have a spare plane, something I know also applies to the Thunderbirds.
In the event of any kind of serious accident, it is likely that displays would be suspended for at least a while, in order to investigate and also out of respect. If all pilots are available when displays resume everything would be normal, using the spare plane if required. If a pilot was out for a short time they might fly the 8-plane display. The Arrows fly standard planes with minimal modifications, so presumably a new one could be readied fairly quickly.
In 2010 when Flt Lt. Ling was injured too badly to continue with display flying he was replaced by a pilot who had already flown with the team in a previous season. There was sufficient time before displays recommenced to make the "new" pilot current and safe.

The other problem with having a reserve pilot is that he or she would have to be able to replace any one of the first-choice pilots, so would have to know all the parts instead of just one.

In 2010 when Flt Lt. Ling was injured too badly to continue with display flying he was replaced by a pilot who had already flown with the team in a previous season. I'm not going to dispute facts (which I assume this is), but this part doesn't make sense to me from an organizational point of view, considering that spare pilots aren't used for fear of not being current and safe enough.

My understanding is that there was enough time while the team wasn't flying displays to get him back up to speed

Recently, the Red Arrows flew with 8 pilots during the rest of the 2011 display season, after the death of Flt Lt Egging - flying resumed at the end of August.  They then lost a second pilot in November of the same year, after the display season was over.  A third pilot left the team prematurely at the start of 2012, so the Red Arrows flew with a unique 7-ship configuration for the 2012 season.  They did not bring old pilots back in either case.

@DJClayworth I know I'm being pedantic but it's not just "temporarily incapacitated" - for a couple of displays in 2014 they flew 8-ship because one of the pilots was attending the birth of his baby (see http://www.bournemouthecho.co.uk/news/11449245.Red_Arrows_baby__It_s_a_boy_/)

This is a great answer so far, I wish we had some sort of information to either say the US teams did the same or they are different in some way.

Similar to what happened in the aftermath of this 1999 crash, I would anticipate that the Navy will bring back one of the former team members to replace Capt. Kuss when the Navy and the team are ready to resume flying.

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text:
Is it possible to land a commercial aircraft with an elevator trim stuck at a high degree?
I know this is not practical (considering there is normally not much use to use up to 30 degrees of elevator trim), but if you were on a Boeing 777 or 737, or similar, and the elevator trim was set into said position, and stuck there, would it be possible to safely land said aircraft in that condition?

The answer is a resounding Yes! You can safely land an aircraft with Elevator Trim jammed either up or down.  Maintaining straight and level flight with Elevators alone can be difficult because the aircraft is sensitive to other conditions, airspeed, wind, etc These can be compensated for through the use of Trim. Trim is a much smaller version of an Elevator, often adjusted up or down by a small wheel between the front seats.
Use of trim can give you much more stability by making smaller adjustments so the Pilot doesn't need to fight the Elevators to maintain height.
During takeoff or landing the affects of a jammed trim can be compensated for by applying small amounts of opposite Elevator.

@ymb1, most jets, B737 included, don't have trim tabs on elevator. The trim control in cockpit controls the stabilizer pitch. So elevator trim is the same as the stabilizer in the question.

@ymb1, right; I read your comment and didn't read the answer well. Yes, the answer is totally wrong. I don't agree a stuck trim tab would not be as big issue though; basically whatever the trim mechanism, it needs to produce similar forces for the pilot to overcome.

@ymb1 The question didn't mention Stabilizer at all. My answer may not have be complete but it is still correct, you can easily overcome a stuck trim tab. It will affect control, but you can land safely - that was the question.

@ymb1 See the Aircraft section here https://en.wikipedia.org/wiki/Trim_tab for some more information.

@ymb1 I agree, there are alternatives and your accepted answer is spot on. My answer expanded slightly. I read the question as being "more general" and 737 was mentioned only as an example.

@AdmiralNoiseBottom, the problem is that trim tabs don't affect the authority of the elevator, only the control forces, the movable stabilizer does affect authority. So the general statement you make for trim tabs does not apply and can only be made with specific reference to the design in question.

@JanHudec agree in the context of 737/777 however I believed, perhaps wrongly, the question was more general. :)


text:
What is an aileron bushing?
What is an aileron bushing,and what's its use?

Bushings are a type of bearing that has no rotating parts. They are among the oldest bearings known.
There is nothing special about it being for ailerons, except that is will be installed on the hinge of an aileron.


text:
How is shear stress distributed on an airfoil?
I know the pressure distribution on an airfoil but not shear stress. How is shear stress distributed on an airfoil?

How are you defining shear stress in your question? Front to back? Inboard to outboard?

Inboard to outboard

Shear stress is proportional to the speed gradient at the wall. This means:

A thin boundary layer produces more shear than a thick one. The boundary layer is thinnest right next to the stagnation point and grows in thickness downstream.
A turbulent boundary layer will create much more shear stress than a laminar one. Most of the shear on an airfoil happens past the transition point.
Higher speeds cause higher shear stresses. Therefore, the suction area on the upper side of the airfoil produces more shear stress than the pressure area on the lower side. In a separation bubble with speed reversal at the wall you will even get a small amount of "shear thrust".

The shear acts along the local flow direction, so it is mostly front-to-back. Only near the wingtips, where lateral flow becomes non-negligible, will a lateral shear component become noticeable.

Friction drag over chord for an E502mod airfoil at 3° AoA. Blue: Top surface, Red: Bottom surface. Source: XFOIL 6.97. The transition points are clearly visible: It is where shear shoots up again at mid-chord. Note the separation bubble ahead of the transition point on the bottom side: It is marked by negative values of shear.

For clarification, @DavidTeahay this is the exact answer to the question as worded. But, at first read, I thought the question was more about the shear distribution over a wing. Shear and moments would be used for rib/spar configuration and sizing analyses. FYI. Sorry to bother if you already know the difference. ;)


text:
How I determine numerically the roll rate of an aircraft?
I'm a Spanish student of aerospace engineering and I'm doing my final bachelor work that consists in designing an unlimited aerobatic plane, and I wonder if it is possible to calculate an approximation of the roll rate depending on design parameters. ( I have aerodynamic analysis of the wing, CL, CD, MAC, W, ...)
And another question about it, how exactly the trailing edge sweep angle affects the stability? And some bibliography?

Welcome to aviation.SE!

Welcome to Aviation.SE. I'm not sure, but I feel that the second question is not completely related to the main one, so it might be better to ask it with a separate post.

If you're in the ETSIA, you should go to the hangar building and ask whoever taught you Flight Mechanics I & II :P

In order to determine the roll rate of an aircraft, all you need to do is to set the rolling moment from aileron deflection equal to the roll damping of the wing (actually, of the whole aircraft, but the wing dominates roll damping anyways). So you set
$$c_{l\xi}\cdot\frac{\xi_{left}-\xi_{right}}{2} = -c_{lp}\cdot p = -c_{lp}\cdot\frac{\omega_x\cdot b}{2\cdot v_{\infty}}$$
$$\Rightarrow\omega_x = -\frac{2\cdot v_{\infty}}{b}\cdot\frac{c_{l\xi}}{c_{lp}}\cdot\frac{\xi_{left}-\xi_{right}}{2}$$
The symbols are:
$\kern{5mm} \xi\:\:\:\:\:$ aileron deflection angle
$\kern{5mm} v_{\infty}\:\:$ velocity
$\kern{5mm} b\:\:\:\;$ wing span
$\kern{5mm} c_{lp} \:\:$  coefficient of roll damping, using $\frac{b}{2}$ for its reference length
$\kern{5mm} c_{l\xi} \:\;$ coefficient of rolling moment due to aileron deflection
$\kern{5mm} p \:\:\:\;$ dimensionless roll rate
$\kern{5mm} \omega_x \:\:$  rolling speed in rad/sec
Damping decreases with altitude, and in this equation the increase of flight speed with altitude will make sure that roll damping decreases accordingly.

Hi, I guess the question is also related to the geometric design parameters involved in roll rate, although the criteria you give definitely helps decide the required roll rate. Maybe, the answer can be expanded to include maneuver speed, max roll rate attainable, time to bank, and their relationship with the geometry and location of the ailerons, and maybe aileron tabs.

@GürkanÇetin The geometric design parameters are reflected in the coefficients. By the way, the answer does give the max roll rate attainable.


text:
What was the first plane that allowed walking during flight?
What was the first plane that allowed crew members and/or passengers to stand and walk during flight?
P.S. I mean walking inside the cabin, as part of normal operation intended for by the plane designers, not walking outside the plane, on wings and other acrobatic activity.

I assume that balloons are excluded for this question. If balloons were to be included, the first person to walk around while in flight would have been Jacques-Etienne Montgolfier in 1783.

@PeterKämpf you mean Jean-François Pilâtre de Rozier? The date of Etienne Montgolfier's ascent is somewhat in question, but the date I had was October 15, 1785 while de Rozier's ascent was on November 21, 1783. The balloon that de Rozier used was made by the Montgolfier brothers.

The first airplane with a cabin big enough for walking around was indeed a Sikorsky. This was the Sikorsky Russky Vityas, also sometimes named "Le Grand", a name which was given to an earlier, two-engined version. Oh, and the cabin included a washroom, too!

Sikorsky Russky Vityas (picture source)
It was the first four-engined airplane in the world and the biggest airplane of its time. It flew first on May 10 (or 13, depending on the source), 1913.
Quote from Wikipedia:

After the Russky Vityaz's first test flights between 10 and 27 May
  1913 (Old Style dates), it was established that a passenger could even
  walk around the cabins without causing any problems to stability.

Early Le Grand version with two engines (source)

Walking around was always allowed. Allowing passengers to play tennis took more technology:

Meals and table service arrived around the same time, 1924, for this Curtiss JN-4:

I was asking about walking inside cabin, not some sort of acrobacy. One can walk on wings of any plane, there is no need for the plane to provide for it.

In the early days (before we made people get up to keep the blood flowing) the only real reason to get up on a plane would have been to go to the bathroom. That being said the first plane with a bathroom was the Caproni Ca.60 Transaereo although it crashed on its second flight. The Handley Page H.P.42 is considered the earliest plane to have a toilet built in 1928.
The other way to look at this would be to consider the first plane that allowed people to walk around if just to stretch. Early airlines like the Short Empire 1936, or the Boeing 314 Clipper 1938, most likely saw regular walking around on their long flights but these still post date the HP42.

I doubt it was the first to allow walking inside cabin.

What was the first plane that allowed crew members and/or passengers to stand and walk during flight?
What I know is that by 1913 people were already standing during flights (see the picture).

Russian plane Sikorsky Ilya Muromets ca. 1913

I am asking about walking inside cabin, as a part of notmal operation, not acrobatics or shows.


text:
Are nearest VOR stations always tuned to?
I am flying under IFR.
My current leg route is Z401. I am between TIPRU and VOR VLM (VLASIM). I am on inbound radial 304° VLM:

This is an RNAV route. But let us imagine it is non-RNAV and I am flying a non-RNAV plane.
On the NAV1 receiver I tuned and checked I have VLM.
I have a spare NAV2 receiver. Should I tune on NAV2 the nearby VOR VOZ (VOZICE)? If yes, why?
I assume not, unless I am flying  RNAV plane which will utilize it as source of position. Even then I am not sure if I should tune it.

Your example is a bit confusing because it seems to be a GPS-based route, it may be better to a look at a more 'realistic' one, where you're using only VORs for navigation. The reason to tune a second VOR is to cross-check your position, either by crossing a specific radial or perhaps by using DME (for a VOR/DME or VORTAC). If that's useful to you then you should definitely tune it.
Here's a US example. Let's say I'm flying eastbound on V241 from the SJI VORTAC following the 081 radial outbound. I've tuned the SJI VORTAC on NAV1, but I have no DME or GPS:

ATC tells me to "report LOXLY", which is 29nm from SJI but I have no DME so I can't report based on that. However, LOXLY is at the intersection of the SJI 081 radial, the BFM 052 radial (BROOKLEY VORTAC) and the NUN VOR 305 radial. That means, on NAV2 I can tune either BFM 052 or NUN 305 and when both the NAV1 and NAV2 needles (as it were) are centered, I'm at LOXLY. You might also notice that the PENSI intersection to the east is defined not only by VOR radials but also by the localizer on runway 17 at KPNS.
In this example, two VOR radials are needed to identify the fix (assuming no DME and no GPS) but you could tune a second VOR even if it isn't required for a named fix, to manually check your progress along your route (see chapter 7 of the FAA Instrument Flying Handbook). You can also time how long it takes to cross two radials on the off-airway VOR and use that information to calculate the distance to it, as a sort of 'manual DME'.
Having said all that, if you don't need or want position information from the second VOR there's no reason to tune it. But especially if GPS is your primary navigation method it wouldn't hurt to stay familiar with them as a cross-check and even as a fallback in case GPS becomes unavailable (which is not unusual).
(As Carlo Felicione mentioned, you could use just one NAV radio and switch back and forth between two VOR frequencies, but that's rather awkward and not something that most people would want to do in normal circumstances.)

In truth, the minimum navigation equipment required to identify the course and waypoints you suggested is a single nav radio and OBS/HSI/RMI, though it will require you to periodically change frequencies and selected bearings to do so.

@CarloFelicione Yes, indeed. I've added that to my answer and made a couple of minor changes to avoid confusion about "VOR" sometimes meaning a NAV radio (which isn't technically accurate, but it is common)

Assuming you are using VOR's for IFR in-flight navigation.
You wouldn't just tune to the nearest VOR, you would tune to a VOR on your route and follow a radial inbound.
Once you cross over the VOR, you would follow an outbound radial until such point that you are within navigational signal strength of the next VOR on your course.
I'm not completely understanding your question, can you potentially rephrase or give a situational example to what you mean?

I rephrased my question

Assuming those are victor airways at the position you suggested, tuning your second nav radio to VOZ at 116.95 would not be necessary to navigate that route, though you could do so if you needed to locate your position on the airway or get an estimate of your flight time to the VLM VOR/DME, if you did not have a functioning DME or GPS on board.  You could also use the second nav radios as an additional indicator of when you passed over the VLM VOR/DME instead of simply flying blindly through the cone of confusion and waiting for the flag to change from TO to FROM.
These techniques also can be done with a single OBS as well, albeit it requires frequently changing nav frequencies and OBS settings.


text:
How does pressure increase in a multistage compressor?
Given the overall pressure ratio of a multi-stage compressor, how can I calculate the increase in pressure at each stage?
Does pressure increase linearly at every stage, or does it increase logarithmically or exponentially?
Intuition tells me that pressure increases logarithmically since the latter stages of a compressor can't compress the air as much as the first stages, but intuition hasn't served me so well in thermodynamics...
Thanks!

you can increase the later stages' efficiency by decreasing the area through which the air goes most turbine engines will do this

That makes sense, but how does that affect the increase in pressure?

Firstly, your intuition doesn't really apply in terms of basic thermodynamics (but, as I'll explain, you're kind of right):

Boyle's Law: "For a fixed mass of gas, at a constant temperature, the product (pressure x volume) is a constant."

Pressure does increase linearly [assuming the temperature stays the same]: if you squash an amount of a gas into half the volume, the pressure will double (assuming you keep the temperature the same). If you squash it into half the volume again, the pressure will double again (4x the original)
However you're also right in that we don't simply increase pressure by the same amount as we go along: Each stage compresses the air by a different amount (otherwise an engine would look like a weird triangle). and perhaps more importantly we can't maintain a constant temperature in an engine... as we compress the air into a smaller volume the temperature increases unless the air is being cooled in some way.
Essentially, though, you can calculate the pressure change at each stage if you know how much the volume reduces by (ie how much smaller each chamber is than the last) and the temperature of the air in each.

Exactly. it depends on how each compression stage is designed.

I forgot about Boyle's Law! Unfortunately, I don't know the change in volume or the design of the compressor stage, so I can't use it.

For a fixed mass of gas The mass of gas is not fixed though, is it ? You can augment the pressure of a fluid in a conduit while maintaining a constant section by "slowing it down". Bernoulli's_principle

@YaJBoy, the mass is always fixed, because mass is (in and off itself in a non-relativistic case) a conserved quantity. You use conservation of mass to relate the velocity with cross-section. Then you use conservation of energy (a.k.a Bernoulli's equation) to calculate the pressure. Assuming the density changes are negligible, you can solve the equations in that order, but if the pressure changes are large, you need to throw in the adiabatic compression equation and then you get a set of three equations. Of course an engine then adds some non-adiabatic expansion.


text:
Why is the UH-60 tail rotor canted?

The Sikorsky UH-60 (S-70) has a tail rotor that is canted 20 degrees upwards. Why is that?
Picture source

John K and Koyovis's answers are both correct. However, as a former pilot of the UH-60 and a mechanical engineer here is a simpler version.
A helicopter must be balanced. If the front is much heavier than the tail, then it can't fly safely as the nose is too low. If the tail it too heavy, then the same. The point of balance is called the center of gravity.
The tail boom on a helicopter is very long. If you were to add one pound to the tail vs one pound to the nose, the pound on the tail would more impact due to the length of the tail boom. In engineering this is called the "moment arm" By canting the tail boom, the tail rotor actually lifts the tail boom. There isn't that much lift, but since the tail boom is so long it has a pronounced effect. This gives the aircrew more latitude in loading the helicopter. With the extra lift provided by the tail rotor, we can put more load (troops, fuel, etc.) behind the rotor mast and still keep the center of gravity in acceptable limits.

I added explicit links to "both the previous answers", since it's hard to work out exactly which answers those are on a page that now has four answers. Note that answers can be displayed in different orders for different people, and votes can change the order, too.

A guy in my glider club used to fly them.  It's something to do with achieving a vertical lift component of several hundred pounds from the tail rotor's thrust, and that and the large horizontal tail allow a large C.G. range by helicopter standards, as well as adding a bit to the total vertical lift capability.  You could say that it turns the machine into a sort-of quasi tandem rotor helicopter, with just a little bit of tandem-ness.
There is some kind of mixing system in the control system to deal with various cross coupling effects due to interactions between the tail surface and the canted tail rotor and main rotor, but which is transparent to the pilot.
I snooped around and found a paper that talks about the advantages of canted tail rotors here.

That paper is an interesting read.  Kind of un-intuitive.  Isn't it kind of like using a strongly lifting tail on an airplane, in a way?  One's first reaction is that the best thing for the tail rotor to do would be to just counteract torque, not also help with lift.  I guess if you have this big complicated transmission anyway, it's more efficient to use it for more than just one thing...

I came across this in Ray Prouty's book, Helicopter Performance, Stability and Control.

The best position for the centre of gravity on a single rotor helicopter is slightly ahead of the main rotor shaft.
In some cases, (an) aft C.G. position is forced by design considerations even during preliminary design.A classic example of this is the Sikorsky UH-60A. As explained in reference 10.13, this helicopter was limited in overall length by the requirement to load it into a C-130 without major disassembly. With the rotor sized by the vertical climb requirement, the air transportability requirement dictated a short nose. This and the desire to carry all the fuel behind the main cabin, led to a centre of gravity range of more than 15 inches, all located aft of the main rotor. Sikorsky more or less satisfactorily solved the resultant trim problem by canting the tail rotor, as explained during the discussion of tail rotor design.

Note that in the design phase, it would have been a lot simpler to shift the CoG forward by constructing a longer nose, but this was not possible and the more complicated canted rotor option had to be implemented. With a large useable range of CoG as a result.
Downside: the canted tail rotor introduces cross coupling between yaw and pitch, but since there are two control mechanisms for pitch (cyclic control as well) the pitch response to pedal input can be tuned by a control mixer. The stabilator helps at forward speed - it is also in the downwash of the tail rotor and can redirect some vertical tail thrust in the hover.
Upside: tilting thrust at small angles has large trigonometric effects. Thrust in the yaw direction reduces with (1 - cos20) = 6%, at a gain in the pitch direction of sin20 = 34% of tail rotor thrust.

To help trim the lift. The main rotor is (not where it should be) forward of the CG, due to all the fuel being in the rear.

The stabilator has a decided effect on effective lift with the tail rotor. It has a large range of travel, both up and down. This travel combined with the tail rotor thrust augmented by the 20 degree cant makes it a very balanced assembly.
The UH-1 had a limited movement sync elevator mounted forward of the tail rotor arc which provided stability but not increased lift.
This was how it was explained to me by a design engineer with Sikorsky and who was also an Army Aviator.

Gordon Galow the original designer of the helicopter for the US army now 98 years old said it was for the lift. Even at the small percentage angle of the blade it provided some lift. One of the most important components of a helicopters design was it's lift capability. Having in the 1960's spent time trying to develop a replacement for the Skycrane  he designed as much lift into the helicopter as he could possibly get. Gordon Galow was considered one of the best Fluid Dynamic Engineers in the World.

Welcome to Aviation.SE. You can improve your answer if you can find a quote for Galow's statement. Also, part of your answer is not relevant to the question.

In addition to the answer put forth siting Ray Prouty (The Man) tail rotors are canted in order to compensate for the forward tilt of the main rotor mast, allowing for a more level hover attitude.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@Bianfable It looks like an answer to me. If you're saying that it's a wrong answer, then you should downvote.

@DavidRicherby The answer used to say "There is also" and now says "In addition to", which is more of a comment on the existing answers rather than a standalone answer.

@Bianfable I don't see any difference between those two phrasings. In both cases, I interpret it as "I'm not going to repeat what's already been posted", which seems entirely reasonable.

Straight from the -10.
The cant of the tail rotor provides 3% lift (approximately 500 lbs), allows the stabilator to move upward more than if the tail rotor wasn’t canted and also provides a measure of safety by its height.
I only know this as a former Standards Instructor and making up -10 annual
Exams for my crewchiefs.   Greatest helicopter ever made.  Always got me home and with a good pilot, some incredible maneuverability and lifting capacity.


text:
Do flight regulations prohibit sleeping on the floor of an airliner?
During a recent trip in a Finnair A350, a couple traveling together was occupying 1 row of three Economy Comfort seats. During the 12 hour flight, one of the couple stretched out on the seats, the other one on the floor in between the seat rows, leg room being sufficient to allow this.
A flight attendant was overheard stating that sleeping on the floor was not allowed due to safety regulations. What safety regulation would prohibit this?
update
During cruise condition, no Fasten Seatbelt sign. EASA regulations. Yes you're out of your seat but we're allowed to walk around aren't we. Where is the hard, written, safety regulation?

Regardless of regulation, it's not a good idea

I don't know how the regs might differ, etc. I slept across a row of seats that were technically jumpseats in a 747 cargo jet. I don't think I buckled in while lying down. There were off-duty pilots on board and they never said anything. I was sitting up for t/o and landing.

@TomMcW The cockpit and jump seat culture of cargo operations has certainly changed greatly from my 727 and 747 days in the 1980s and 1990s. It was pretty relaxed back then, at least at the two freight carriers I flew for. We didn't care back then where people slept or stood, and whether they wanted to use a seat belt or not. We used to have jumpers stand in the cockpit for takeoff and landing and nobody minded except for the occasional hard-ass captain. Another trick was to sleep in a ULD that had soft contents.

@Simon and "Safety regulation say so" is much stronger argument than "it is not a good idea at all" however the reasoning is good. The first one is much more foolproof.

@Terry I'd be afraid to sleep in a container. They'd forget I was there and I'd end up in Hong Kong or something.

@TomMcW that would be handy, if Hong Kong is where you wanted to be! :)

Yuck! The floor is where everyone barfs!  There is probably not an infectious disease regulation, but there should be.

The sleeping on the floor prohibition is on air France's safety cards http://my-safetycard.de/index.php?page=searchsafetyscan&q=22371

@mongo in theory the carpets should be cleaned, at least routinely if not after every flight. Not sure how/how often this happens, however.

@toonarmycaptain I suggest talking with someone in public health or someone who has a microbiology background. The carpet in a transport plane is probably dirtier than the lavatory sink, counter and floor.  Truly cleaning and disinfecting carpet is problematic. Carpeting is vacuumed periodically, and perhaps shampooed less frequently, but it is never clean enough where it would be advisable for sleeping on.

Essentially this has been explained to me as "you're a trip hazard." '
Additionally, inferences that if power/lights go off, you'll be stepped on and trip people, particularly people in your row (don't know how this applies so much if you're a couple/by yourself), and in the way in the necessity of evacuation, or in the case of a flight attendant needing to rush to the window to look out. How they'd do that with your legs in front of you in a seated position, I don't know.
I do know it's not allowed on QANTAS (and Jetstar), Emirates, American, Virgin Blue, or North West (now defunct). In my experience it's pretty common to hear the captain or stewardess announce or tell a passenger if you're on an overnight or long flight.
ADD: Just  got off a QANTAS flight, this is more of less what they said. The flight attendants need to be able to rush to a window or an overhead locker/passenger in a window seat in an emergency situation, so bags cluttering floors, people sleeping on floors isn't ok. Also mentioned was the danger to passenger in case of turbulance, etc, the comparison with sleeping on the back seat floor of a car in motion was mentioned vis a vis unexpected swerving or breaking.

Wow, the person on the floor would be almost as much of a problem as a tray table, inexplicably 12 foot long headphone cable, blanket, backpack by feet, coat across lap, kicked off shoes.... : )

We also tried those inflatable cushions that act as seat extensions, filling the gap in front of the seat, for the kiddos to sleep - the flight attendants had no issue with these.

That depends on the air carrier and the regulatory body they're certified by. Finland is part of the EU so I'm assuming that Finnair's certificate is under EASA aviation safety regs. Specifically, a quick Google search finds:

CAT.OP.MPA.165 Passenger seating:
The operator shall establish procedures to ensure that passengers are seated where, in the event that an emergency evacuation is required, they are able to assist and not hinder evacuation of the aircraft.

Finnair would also write their own SOPs to ensure they meet all the EASA regs.

"in the event that an emergency evacuation is required" doesn't seem to be the context of the question (cruise mostly)

Well, in case of emergency it is way to easier to just fasten your seatbelt and put the mask on compared to stand up, get yourself in the seat and fasten your seatbelt... In case of decompression every second matters and only few people would remember what is right (and counterintuitive, if you don't know what's happening) to do.

@ Crowley these are valid arguments, but equally valid for passengers walking to the pantry, being in the toilet etc.

This will vary based on jurisdiction and the stage of the flight, but in the US under the FAA this is prohibited (most likely for multiple reasons) for at least some stages of flight and flight conditions. This is most likely an EU issue but here in the US...
They can't do it during taxi take off and landing:

§ 121.311 Seats, safety belts, and shoulder harnesses.
(b) Except as provided in this paragraph, each person on board an
  airplane operated under this part shall occupy an approved seat or
  berth with a separate safety belt properly secured about him or her
  during movement on the surface, takeoff, and landing.

And the flight attendant was well within their rights if the fasten seat belt sign is on thanks to

§ 121.317 Passenger information requirements, smoking prohibitions,
  and additional seat belt requirements.
(f) Each passenger required by § 121.311(b) to occupy a seat or berth
  shall fasten his or her safety belt about him or her and keep it
  fastened while the “Fasten Seat Belt” sign is lighted.
(k) Each passenger shall comply with instructions given him or her by
  a crewmember regarding compliance with paragraphs (f), (g), (h), and
  (l) of this section.

I'm still looking for the letter of the law on if you need to be seated in an approved seat during the cruise stage of flight with the "fasten seat belts" sign off.

In cruise condition, fasten setbelt was off.

With that in mind. That may actually be permitted here in the US but I will continue to look.


text:
How does a turboprop engine keep running during thrust reversal?
For thrust reversal after landing, a turboprop engine reverses blade pitch and blows air forward. But the engine itself requires air flow for the turbine.
How can a turboprop engine keep running when the prop blows air away from it?

upvoting because, while obviously the turbine keeps ingesting air, I'm hoping someone will find a good flow-field visualization.  I haven't so far.

most of the blowing happens on the outer part of the blades; their twist distribution means that the inner part is stalled and does litte to suck air away from the intake.

The prop is not blowing air away from the intake, atleast in that region. In modern propellers, the twist of the blades is such that the blade angle is smaller at the tip compared to the root.

Airfoil section in propeller blade; image from FAA Pilot's Handbook
Now, if reverse thrust is applied, the outer regions of the propeller is in the negative angle of attack, producing reverse thrust. However, the case is different in the root region, which won't have a negative angle, thus not blowing air 'away'. The net result is that the compressor can quite easily handle the reverse thrust condition.

Propeller angles in various flight regimes; image from pilotsofamerica.com
Another thing is that the reverse thrust is quite small compared to that of the forward flight and the speed is also quite small. modern compressors don't have much problem in this regard.
For comparison, consider the turboshaft engines in the helicopters in rearward flight- they can handle a much greater range of speeds in that condition. As an extreme case, consider the Russian aircraft doing tailslide- even the turbofan engines cope up with that, albeit in a much limited manner.


text:
What exactly happens when power is reduced in trimmed, straight and level flight?
I understand that trimming an aircraft at a particular airspeed e.g. 100kts will keep the aircraft flying at that airspeed (100kts) even if you were to e.g. Lower power. This is apparently accomplished by the pitching down of the trimmed aircraft.
But I am not too sure if I understand the rationale behind the pitching down. I hope to seek advice on whether what I understand is correct:
When you elevator trim to fly unaccelerated straight and level flight (all forces balanced) at e.g. 100kts, you are relieving the pressure needed to keep your aircraft in that angle of attack that produces enough lift to counter the weight, at that particular airspeed (because any increase or decrease in airspeed also will affect lift, so speed will affect the amount of lift that needs to be created by the AOA to counter the weight so as to stay level). So if your speed starts to drop, the amount of lift that your AOA must make = increased. But since you have trimmed elevator to that position means the AOA is fixed. So what happens is that the aircraft will pitch down (trade height which is potential energy for kinetic energy so your speed increase), then your speed will be back to what it used to be and your that trimmed AOA will continue to be able to supply that exact amount of lift, which together with the lift at that same airspeed is just right to counter the weight. So the aircraft will be back to level flight again.
Since power is lowered, I would expect the aircraft to continue to lose speed and the whole cycle of pitching down then back to straight and level will go on and on.
Does this make any sense?

You are very perceptive to note that for a given angle-of-attack, a return to the exact airspeed that allowed level (horizontal) flight would indeed imply a return to level (horizontal) flight.  But that's not what we expect to happen when we reduce the power.  Hopefully this answer will help you to understand why not.

When you elevator trim to fly unaccelerated straight and level flight
  (all forces balanced) at e.g. 100kts, you are relieving the pressure
  needed to keep your aircraft in that angle of attack that produces
  enough lift to counter the weight, at that particular airspeed

Exactly right.

(coz any increase or decrease in airspeed also will affect lift, so
  speed will affect the amount of lift that needs to be created by the
  AOA to counter the weight so as to stay level)

Technically this is not quite right.  The amount of lift that is required for the flight path to stay level rather than bending up or down is the same at any speed, but the AoA needed to create this lift varies with airspeed.  Maybe that's what you actually meant to say, or something close to it.

So if your speed starts to drop, the amount of lift that your AOA must
  make = increased.

It may be that the word you are looking for is not "lift", but "lift coefficient".  Increasing the AoA increases the lift coefficient.  Lift is proportional to lift coefficient times airspeed squared.  To maintain horizontal flight as we slow down, we need the same amount of lift, which means we need a higher lift coefficient, which means we need a higher AoA.
Or maybe you simply meant to say something like "if we hold angle-of-attack constant and decrease airspeed, then lift will be decreased, which means lift will have to somehow be increased again to bring things back into balance."  This is exactly true, regardless of whether that "somehow" involves an increase in angle-of-attack and lift coefficient, or a return to a higher airspeed at the same angle-of-attack and lift coefficient that we had before.

But since you have trimmed elevator to that position means the AOA is
  fixed.

Yes, at least to a first approximation.  We'll assume that is exactly true for the purpose of this answer.

So if your speed starts to drop

The speed is dropping because we've reduced power and thrust, so drag is greater than thrust, temporarily causing the net force acting along the direction of the flight path to be non-zero.

the amount of lift that your AOA must make = increased.

Yes, the drop in speed has caused a loss of lift, and lift must somehow be increased again to bring things back into balance.
In the meantime, lift is temporarily less than weight.  There is now a net force acting perpendicular to the flight path (i.e. downward), so the flight path bends (curves) downward.
Since the angle-of-attack stays constant, as the flight path bends downward, the aircraft must pitch down.
As the flight path bends downward, gravity (the weight vector) gains a component that is partly acting parallel to the flight path in the forward direction, and this is what drives the increase in airspeed till it is approximately back at the initial value.
As the airspeed increases, the flight path stops bending down.  Actually in real life we are likely to see the airspeed slightly "overshoot" and then decrease again.  As the airspeed "overshoots" it provides the excess lift needed to curve the flight path up toward something closer to horizontal flight-- but not exactly horizontal.  Since you've reduced power, you'll end up in a descending glide.

then your speed will be back to what it used to be and your that
  trimmed AOA will continue to be able to supply that exact amount of
  lift

Since you've reduced power, you are now in a descending glide.  To a first approximation, your statement above is true.  It is a good approximation for shallow to moderate glide angles.  But if you want to know the full truth, it is that the lift vector is slightly smaller in a glide than in level flight, which means the airspeed is slightly lower in a glide than in level flight at the same angle-of-attack.  For more, see the vector diagrams in this related answer.  But you really don't need to understand this to answer your question.  The most important thing to understand is that being in a glide rather than in level flight is the only way we can accommodate the fact that drag is now greater than thrust.  Again see the vector diagrams in the linked answer-- just mentally substitute "drag minus thrust" for "drag" in the vector diagrams and you'll get the idea.

which tgt with the lift at that same airspeed is just right to
  counter the weight. So the aircraft will be back to level flight
  again.

No, it will be in a stabilized glide.  The weight will be balanced by the vertical component of lift, plus the vertical component of (drag minus thrust).  See the vector diagrams in this related answer for more; just mentally substitute "drag minus thrust" for "drag".

Since power is lowered, I would expect the aircraft to continue to
  lose speed and the whole cycle of pitching down then back to straight
  and level will go on and on.

You are starting to touch on the question of the pitch "phugoid" oscillation but that really has nothing to do with the core of your question.  The most important thing to understand is that reducing the power while holding angle-of-attack constant-- or while holding airspeed constant -- technically both cannot happen at once but don't worry too much about that-- will allow the airplane to end up in a stabilized glide, with the weight supported by the vertical component of lift plus the vertical component of (drag minus thrust).
A couple of more notes in closing--
First, this business about the aircraft tending to trim to a slightly lower airspeed in a glide than in level flight, if angle-of-attack stays constant -- you'll rarely be able to detect this effect in actual practice.  For example, in an airplane with a propeller on the nose, if you change the power setting without touching the yoke or the elevator trim control, the change in the propwash over the tail will often cause some amount of change in angle-of-attack, which will drive a change in airspeed.  In jets, offset thrust lines can cause a similar effect.  These sorts of effects are likely to completely dwarf the change in airspeed caused by the fact that for the same angle-of-attack, the lift vector, and therefore the airspeed, must be very slightly smaller/lower in the glide than in level flight.  Note that in the vector diagrams in the answer linked above, the lift vector is really not very much smaller than the weight vector as long as the glide angle is not too steep.  And since lift is proportional to airspeed squared, only a very small reduction in airspeed would be needed to cause that amount of reduction in the lift vector while holding angle-of-attack constant.  Still, when the (drag minus thrust) vector is not zero, it must be accommodated in the vector triangle as shown in the linked answer, which means that lift must in fact be a little less than weight.
And second, if you make your power reduction very gradually, the aircraft will stay close to a steady-state condition.  You'll smoothly transition to the final steady-state glide and final airspeed (which for all the reasons noted above, may or may not be a little different from the airspeed you had at the higher power setting).  On the other hand, if you abruptly make a large power reduction, you'll see the airspeed drop significantly, and then the nose will pitch down quite far, and then the airspeed will "overshoot" well above the final steady-state value, and then the nose will rise above the final attitude for the glide, and then the airspeed will "undershoot" the final value.  This is the pitch "phugoid" in action, and you might see several cycles before everything settles down into the steady glide.

Your last paragraph makes a very good point.  In a 172 the reduction in trim speed from going to cruise power to full power can be several kts in my experience depending on the CG location.  When adding large amount of power I got in the habit of applying a little tweak of trim to compensate right away.  I used to play around in a CRJ Flight Training Device (no montion/visuals fixed simulator, but otherwise the same as the Level D) and observe trim changes with thrust.  With the tail engines, adding thrust added a few kt to trim speed, if you had the patience to wait for the phugoid to finish.

(Thnx, now refers to second-to-last paragraph as one more has been added.)

This makes sense and is approximately what happens if you reduce thrust during trimmed straight and level flight. The aircraft will go though a series of damped oscillations, called 'phugoid' until it finds its new equilibrium state. The new state will be the original airspeed, but now in a constant descent.

Hello! Thanks for your reply! So the new state will be a constant descent and not a series of straight and level followed by descent then back to straight and level followed by descent and so on?

The end state will be constant descent, but the transition will be a series of pitch/vertical speed oscillations that will dampen out (in stable aircraft). The period of the oscillation will vary between aircraft, generally the bigger the aircraft, the longer the period. The damping factor is low, it can take along time to settle at the end state.

Seems like you have a misconception there: When the vertical component of lift equals weight, this doesn't mean the aircraft will fly level. When the forces balance out, the vertical acceleration will be zero, and thus the vertical velocity will be constant (not necessarily zero).
So after the initial disturbance and the resulting phugoid oscillations (where vertical acceleration oscillates between positive and negative) die down, the aircraft will be in a new equilibrium with zero vertical acceleration and thus a constant rate of descent.

Thanks for your reply! I believe in a state of unaccelerated straight and level flight, vertical velocity will also be zero isn't it?

Yes, it will, but only in that case (level flight).

In Simple Terms ....
Pitch controls speed.
Power controls speed and lift. Increasing power for the same angle of attack will produce more speed and hence more lift. Decreasing speed for the same angle of attack will produce less lift.
If you reduce power only and keep pitch the same, then you will lose lift and speed. If you were flying level before, then now you're sinking.
Yes - in reality its way more complicated than this. Its a dynmical balance between all of the controls on your aircraft. If you pull back on the stick then speed gets converted to height until drag washes it all away and you stop climbing. If your center of thrust is not directly in line with the center of drag, then the pitch will change as power changes. (This why 737 Max's crash)  Increasing speed increases drag which makes the aircraft less efficient. If you pitch down to maintain speed, then drag goes up and you sink even faster.
Power changes and pitch changes are dynamic forces and most aircraft you will ever fly will stabilize somewhere new. Some take longer than others. Most will tend to wobble about a little till they settle. Don't let go of the stick - look out of the window at the horizon.
If you really want to get a feel for how lift and speed are related, go fly a sailplane for a few hours.

Welcome to ASE.  But, "If you reduce power only and keep pitch the same, then you will lose lift and speed.   If you were flying level before, then now you're sinking."--  If you are sinking while holding pitch attitude constant, you've changed angle-of-attack, which the original question suggested should stay constant.  The original question was phrased in a way that was based on a constant elevator position (or at least trim setting), not a constant pitch attitude.

Well, to be fair, the question appears to be posted by someone who may not clearly understand the difference between the true angle of attack and the pitch of the aircraft.
So yes, the answer is heavily simplified. If you reduce power and don't touch the trim, you'll sink and slow down. You push forward to keep speed up ( or not, you're the pilot).

@dalearn-- the guy (or gal) must have chose to put those words in caps for some reason, don't you think?  Why take them away?


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Does altitude affect how you interpret the attitude of the aircraft?
I understand that for any specific aircraft, at a constant power setting, you can use the aircraft's attitude as a proxy for airspeed.
For e.g. In aircraft X, when the dashboard is 1 inch below horizon, at power setting X, means the aircraft will be flying at around speed X.
My question is, if you are much higher in terms of altitude, won't your attitude based on visual reference e.g. How many inches away is your dashboard to the horizon, be different when you are much closer to ground?

I would say not significantly, at least not in a small plane.  The horizon is 60+ miles away, you are 1 to 2 miles above the ground (5000 to 10000 feet).  Draw a right  triangle and do the math, you will find the angle is pretty small.  If you go higher, you may find you need more back pressure to hold altitude, but then you are compensating for loss of horsepower with altitude (unless the engine has a turbo to maintain sea level power, most small planes don't).  The other thing you will find is that due to lower power at altitude, airspeed drops, but the thinner air lets ground speed go up.

"... the thinner air lets ground speed go up."  Unless you are facing a stronger headwind!  ;)

Yes, due to the curvature of the earth.  But you'd have just as much variation with a small change in pilot eye position within the aircraft.  The exact "sight picture" of the top of the nose (or the top of the instrument panel) relative to the horizon is not really something that you memorize and use as an absolute reference point with the expectation that it will be exactly the same every time you fly a given airplane.  It's more just something that you keep an eye on to watch for changes.  By the time you've climbed to altitude, you've had plenty of time to (perhaps unconsciously) get used to the resulting slight change in the sight picture between the nose and the horizon line.  All the while, other instruments such as the altimeter or airspeed indicator or vertical speed indicator help tell you whether the place you are putting the nose relative to the horizon, is really the correct place to make the airplane do what you want it to do.  Of course, there many instances where the horizon is not clearly discernible anyway.

Wow this answer is perfect. Thanks so much!

Yes, good answer, but curvature of the earth isn't much of a factor until you are WAY up high...


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What is the approximate range of the Pelegrin Tarragon?
I recently read about the Pelegrin Tarragon ultralight aircraft made in my country, and got interested in it.
Is it possible to have a reasonable estimate of the average distance you could cover in such plane, taking into account that it has a cruising speed of 270km/h, a  96l fuel tank and the engine it uses (a single Rotax 912ULS) is listed as using 15l/h at 5500rpm (75% power)?
Unfortunately, the manufacturer's page doesn't list any max distance or indeed any technical specs, and Wikipedia entry doesn't list much more either

@MichaelTracy dammit, that's what happens when looking from mobile. the manufacturer's page doesn't list range when viewing mobile version of the page. thanks.

Why is this a question when it can be so robustly obtained from a simple Google Search?

That 15l/hr has to be at 60%.  At 75% the specific fuel consumption is under .4 lb/hp/hr, which seems to be a stretch, even for an efficient geared engine.

According to the manufacturer, it has a range of 1,300km.

A more reasonable fuel burn at 75% on the Rotax 912ULS is 18 Lph and with long range 250L option the Pelegrin has a no-reserve range of 3,750 km but few of us would enjoy sitting 13+ hrs in the cockpit. The longer range tanks were developed for a future military trainer incorporating a thirstier turboprop engine.

13 hours... yikes!!!  Nevertheless, welcome to Av.SE!


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Do we need to know the true track to a VOR?
An aircraft can lock onto the location of a VOR and we can see the QDM (magnetic bearing to the station) to the VOR. If this is the case, do we still need to know the true track of that route? And if so, why?
By extension, if we essentially have all we need to get to the VOR in the aircraft, why do we need to know about QTE (true bearing from the station)?
NB: I have no experience in flying a navigation flight

A VOR cannot give you a magnetic heading. It can give you a magnetic track.

Please define QDM and QTE.

QDM - the magnetic bearing to the station. QTE - the true bearing from the station

You can't ask anything from a VOR, its a broadcast only radio.

The short answer is no, you don't need the true bearing to the station if you have magnetic bearing.  Presuming of course that your airplane has a magnetic compass to fly that bearing, there is simply no reason to convert to true.

You don't get either and you don't need it.
The VOR signal gives you a radial to the station. This is normally referenced to magnetic north, because that's what you have on board¹, but it might have been last aligned twenty years ago and so might be a couple of degrees off as the magnetic declination slowly changes over time.
It does not matter what it is anyway. The instrument works so that you select the desired radial and it shows you how far (in degrees) you are to the left or right. You align yourself roughly in reference to the magnetic compass and then you steer right if the needle is on the right or moving to the right too fast and steer left if the needle is on the left or moving left too fast, until you manage to centre the needle.
At that point your heading is something that depends on wind and the misalignment of the VOR. But you know you are following the radial that defines whatever airway or procedure you are flying and that's what you needed.
Note that when the VOR is re-aligned, all the charted procedures have to be updated to the new radials, so they don't want to do it that often. Having the radials off by a degree or two is not a problem, because the heading does not match the radial due to wind in practice anyway and updating all the maps is a lot of work.

¹ A gyrocompass is only self-aligning when moving slowly, so while they can be used on ships, on aircraft the heading indicator is always slaved to the magnetic compass. You can now get true track from GPS, but then you don't really need VOR anyway. VORs exist for aircraft that don't have GPS or their GPS failed.

You do not need the true bearing to the station in order to navigate to it. However, if you don't have a GPS or other NAV equipment on board, you need some way to estimate your groundspeed, and knowing the true bearing can help you do that. Winds aloft forecasts are given with reference to true north, so if you know your own track relative to true north and your wind correction angle, you can deduce your groundspeed with it. You can check this against your resulting calculation of time to the VOR station to confirm it. All of this is important so that you don't run out of fuel. Luckily, having a GPS on board, or even a DME, or even another VOR radio, will allow you to do redundant groundspeed calculations without all the math or winds aloft tables.

The radials extending from the VOR are normally based on local magnetic variation (the compass rose around the VOR on the chart is angled off true by the amount of local variation so that the 360 deg Radial is pointing to the magnetic pole).  The VOR gives no bearing information relative to the airplane; it only tells you that you are somewhere along, or to one side of, a selected radial extending from the VOR, regardless of which direction the airplane is pointed.  But since the radial represents a magnetic track, you fly magnetic headings to orient yourself and and stay on the radial you're on as you fly toward or away from the VOR.
Except.... if you are in the Canadian Arctic, in an area called the Northern Domestic Airspace (the Northwest Territories and Nunavut more or less), the compass is useless because the magnetic pole is right in the middle of it, and everything, airway tracks, runways, VOR compass roses (the few that are up there), are oriented to true.  In that case you fly true headings and tracks, and if you are tracking to the Cambridge Bay VOR, it's radials are also true, and heading information has to come from a directional gyro that is aligned to true heading, and your compass becomes a nice instrument panel ornament.


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Should I fly the true bearing or the magnetic bearing?
If you have a true bearing (track) drawn on your map but at the same time you have the magnetic bearing (as worked out from the true bearing and variation), which do you follow?

the true bearing on your map (and the ground features)
the magnetic bearing (as seen on your compass and to a certain extent, your DI)?

This question is arguably highly opinion-based, and shows no evidence of either prior research or careful consideration of the problem at hand.

This question is flawed because it is based on a fallacy:  It presumes that true and magnetic bearings are mutually exclusive.  They are not.
Every time you fly a track you are following both a true and magnetic course.  They are simply different frames of reference.
So the correct answer is you fly both.  You would normally fly the magnetic heading you computed when you reference your compass, (adjusted for wind) because that is what the instrument displays.
The track you drew on your map is the ground track your airplane should follow if your true to magnetic conversion and wind correction is right.  You will cross check this against landmarks as you go. So, is this track depicted on your chart true (as you imply) or magnetic?  The answer is that it doesn’t really matter, it can be either or both.  It just depends on how you look at it.
It is like the temperature being at freezing, and asking whether it is 0 deg C, or 32 deg F.  Which one do you want to reference?

You fly the magnetic heading if you want to fly any track using a compass, or a DG set to match a compass, because that's your pointing device.  It's providing a magnetic indication, so magnetic headings it is.
If you are flying in the Canadian Arctic or Alaska, different story; the compass becomes useless and all you have is a directional gyro that you set to true heading while on the ground using some ground reference, and try to make adjustments to the DG to compensate for precession as best you can (you will have established that your gyro precesses say 3 deg CCW in 15 min, so you make a 3 deg CW tweak every 15 min and you will still be in the ballpark at the end of your trip).  In northern Canada, all headings and tracks are true above a certain latitude.
Farther south however, you could do the same in theory, but you have the compass available to you so you might as well use it and avoid the hassle of having to make best guess DG corrections.

If you are using dead reckoning, you will need to follow your magnetic bearing including the magnetic deviation. In so doing, you will also be following your true bearing. In the air, you are following your magnetic compass and compass card unless all of your landmarks are within sight of one another. This is incumbent on not having to adjust your heading for wind.
There is no way to authenticate your true bearing except by matching the direct course between those landmarks with your map. This is not so helpful when your waypoints are more than 10 miles apart.

I'm confused-- unless you have travelled so far that you no longer know the magnetic declination, even approximately, the comment about "no way to authenticate" true bearing/ heading would seem to equally apply, or not apply, to magnetic bearing/ heading.

@quietflyer - Sorry for being unclear. My point was that any indications of direction in the aircraft are gained by either viewing a magnetic compass or using equipment (like a DG) or calculations that were originally set or derived using a mag comp. An IRS/INS may be an exception. But, I am not too familiar with them. You would have to use your magnetic bearing in the air. Or, do the math to convert your true heading to magnetic. Otherwise, any long distance dead reckoning could be off. If you are just using pilotage, that’s a different story. Just keep your waypoints close to each other.

Why the "more than 10 miles apart" limit?  Unless you fly where it's really hazy or cloudy, of course.  But in the western US, I can often navigate by landmarks that are 100 miles or more distant.  E.g. once you're past the East SF Bay and can gain some altitude, the Sierra Nevada is pretty obvious.  Mt. Diablo is almost as good going the other way...

@jamesqf - You are quite right in areas of major landmarks. In the South Central US like Texas and Oklahoma, flat terrain would make it more difficult. You would have to rely on bodies of water, major roadways, antennae and turbine farms, oily tank fields, and cities which might be harder to spot 20 miles or more away. To insure you hit your waypoint, you have to use dead reckoning along with pilotage. A little bit more than just pointing the aircraft nose in the general direction of what looks like where you want to go 100 miles away.

My point being, as Michael Hall has stated in his answer, True bearing and magnetic bearing are the same thing with different numbers. They are the same track on your map. The mag bearing just changes with variation. Unless you are using GPS waypoints, in the air, your devices for finding exact direction are going to be based on magnetic compass readings. Even using a directional gyro, it must be reset periodically during the flight. Since your main source of direction is magnetic, so should your frame of reference.

In theory it is up to you whether you want to work primarily in terms of magnetic or true headings/ bearings/ courses.  Obviously if your choice is mismatched to the readout of the instrument you are looking at at a given instant, then you will have to make a mental correction, which can be either merely inconvenient, or disastrous, depending both on the particular situation, and on your competence at such things.  Since there is no way to make a standard aviation magnetic compass give a readout of a true heading,  the normal aviation practice, and arguably the best aviation practice, is to work entirely in terms of magnetic headings and bearings.  Runway headings and AWOS/ ATIS wind direction annunciations and airway bearings on sectional charts and headings for instrument approaches are all labelled accordingly.  Perhaps at some point in our ever-more-computerized future, this practice will be seen as quaint and antiquated.  Setting your directional gyro (if present) to true rather than magnetic heading is always an option if you aren't afraid of the math in comparing to the wet magnetic compass, and if for some reason that's what floats your boat, and if you aren't shooting instrument approaches and landings or talking to ATC.
If you are flying in daylight over a man-made landscape resembling a north-south east-west checkerboard as can be found over much of the central US, and you aren't going to be flying in or above clouds for extended periods or giving headings to ATC or recieving headings from ATC or shooting instrument approaches, there is a significant case to be made for setting your directional gyro to the true rather than magnetic reference frame.  But in such a case you could do almost as well to just "eyeball" your course without ever looking at either the magnetic compass or directuonal gyro.  When it really starts to matter,  in most cases you'll be best off to follow the standard aviation practice and work exclusively in the magnetic reference frame, unless you are flying with computerized displays that can do all the relevant conversions for you at the press of a button, and your contact with ATC is minimal.

future edit-- fix typo in "directional" gyro near end.


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What do the dashed extended green lines on this PFD mean?

The most important source of information for the pilot is the PFD

This is not a Primary Flight Display. It's an MFD, EHSI or similar.

@pericynthion It's referred to as a Navigation Display, or ND.  You're correct that the PFD is something else, with the attitude indicator and airspeed & altitude tapes, etc.

Those are radials off of the HME navaid, which is tuned in both Nav receivers. The two radials displayed correspond to the courses set in the two course select windows.
Putting a navaid's identifier into the FMC "FIX" page can also generate similar bearing lines, although there would be a green circle around the navaid in that case.
An ILS (also the departure runway in the flightplan) extended centerline shows as white, not green, and appears when that ILS (or any other) approach is active in the route, rather than when the frequency is tuned.

Thise dashed green lines appear to be extended center lines for each runway.  Most likely those are the runways with an ILS.

Close, but not correct.

They can't be extended centerlines for two runways because they are converging and you'd never build an airport with almost-parallel runways like that. Specifically, Haneda doesn't have any runways aligned close to the depicted directions.

@pericynthion Tegel airport in Berlin (EDDT) had runways that were not quite parallel... It does exist :)


text:
What regulations apply to a VFR flight from South Africa to Namibia?
I just would like to know what kind of flight plan, permissions, en route airway paths and other factors that need to be considered?
Other than the passport, PPL license and aircraft documentation and so forth.

From what country? If long distance, there is a reason that this would be considered a "really bad idea" by most pilots.

UK to France or USA to Canada

This is very unfocused, there are many, many factors to be considered, and there are different rules all over the world.

You need to file a flight plan for each flight in Namibia, submit a clearance/permit request for your intended route (whole trip) with the Namibian CAA, the clearance number is to be added to your flight plan under item 18, other info, and you need to enter the country via port of entry airports, most practically via Upington to Keetmanshoop.
I have just been flying through Namibia and it is a great country to fly through.

Can you please add some sources/resources to you answer?  Welcome to Aviation.SE!


text:
What is needed to remove my CPL restriction after becoming a US citizen?
I hold a US commercial pilot certificate based on my foreign commercial pilot certificate. This was allowed prior to the ruling that foreign pilots would only be issued a private certificate. On the back of my certificate there is a statement, "Not valid for the carriage of persons or property for compensation or hire or for agricultural aircraft operations".
I am now a US Citizen and I am wondering what I need to do to have this restriction removed.

FWIW, I don't think this has anything (directly) to do with citizenship. It's just about removing the restriction.

You will need to pass the US commercial pilot test to remove the restriction.  If you have enough hours, you may want to consider applying for an ATP certificate.
A couple of things are required to be completed.

Verify the authenticity of your foreign license through the FAA
https://www.faa.gov/licenses_certificates/airmen_certification/foreign_license_verification/
Complete an application for the new commercial or ATP license
Pass the appropriate practical test


text:
What does "mission mixing" mean for long-range aircraft?
I know very little, like long-range aircraft will be used for short-range and medium-range operations. But what is the purpose of using them like that? Also I want to get complete details of "mission mixing" in layman's terms.

Can you please give a source for the term?

Mission mixing appears to be running computer simulations (or other probabilistic analyses) to assess aircraft engine components' reliability also under non-typical or non-designated use. All for the purpose of design or maintenance/inspection strategies, I would assume.
So, mission mixing is not something you would purposely do with actual aircraft. (Or maybe you would, but then it is not called mission mixing.)
Here are a few articles mentioning it:
https://arc.aiaa.org/doi/pdf/10.2514/1.13142
https://asmedigitalcollection.asme.org/GT/proceedings-abstract/GT2012/44731/439/247656
http://en.cnki.com.cn/Article_en/CJFDTotal-HKXB902.017.htm
https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP14812S.htm

Anecdote: In 2018, when Air Berlin stopped flying, the German Lufthansa flew from Frankfurt to Berlin with sixty B747-400. They said it didn't pay off but it was the easiest way to accomodate all the passengers between FRA and TXL. The "program" stopped after five months.


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What is the difference between aluminum tape and speed tape?
What is the difference between aluminum tape and Speed tape? Are these same or not?

Speed tape is aluminum tape that is much thicker with stronger adhesive than the aluminum tape you get at Home Depot, that is approved for temporary application on external surfaces of airplanes.


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Are there design guidelines for sizing vent/surge tanks?
Could someone explain the sizing process of Vent/ Surge tank of Aircraft fuel system? I understand the Vent tank is to collect fuel overflow from the main fuel tanks. The reason could be due to Fuel thermal expansion or fuel over flow during manoeuvre or can be during pressure refueling.
The link
What is the capacity of the vent surge tank in an A320?
discuss about the fuel over flow by Thermal expansion. But can we size vent tank based on the pressure refueling fuel over flow? If so, for how long overflow to be considered? Though it is based on the Vent relief system and flow rates of specific aircraft, requesting any general guideline/ Reference for the design.
Thank you


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Must a CFII be instrument current to provide instrument training?
Can a CFII conduct training for an instrument student in VFR conditions if the CFII isn’t instrument current?

Welcome to aviation.SE! I edited your question to make it a little clearer but if I got something wrong then don't hesitate to edit again or just roll back my changes. I assumed you're asking about the US; whenever you ask about rules or regulations please always tell us which country or regulations you mean. The [tour] may be helpful if you're new to the site.

That... is a really good question!

The requirements for providing instrument instruction are in 14 CFR 61.195(c) and they don't mention currency at all. There are also various FAA legal interpretations on whether or not CFIs (not CFIIs) require an instrument rating to provide instrument training (see this question), and what instrument training requires a CFII in the first place (see this question) and none of them mention currency either.
So no, there is no requirement for a CFII to be instrument current when providing instrument training.
Having said that, 61.65(d)(2)(ii) requires instrument students to do a cross-country under IFR with an instructor. An instructor who isn't instrument current couldn't provide that specific training flight, although obviously the student could use a different instructor. And many CFIIs like to take their instrument students into IMC to let them experience how different it is from being under the hood.
All in all, it's in a CFII's best interests to remain instrument current but it isn't required.

I think it’s best to be current before taking on an instrument student so the CFII is sharp and giving the best possible instruction

@DanielRackley I don’t agree. Everything else being equal, a CFII who is actively training students would be a much better choice as an instructor than someone who is current but hasn’t trained anyone in a while.